1. Field of the Invention
The present invention relates to a controller for controlling an industrial machine, and more particularly to a receiving circuit for receiving information from an industrial machine.
2. Description of the Related Art
In a controller for controlling an industrial machine, such as a numerical controller and a robot controller, external information outputted from the machine is received by a receiving circuit and the received signals are processed by a CPU in a numerical controller for controlling the machine.
FIG. 13 is a block diagram for illustrating an arrangement of a receiving section for external information in a conventional numerical controller. A numerical controller 10 comprises a CPU 1 for generally controlling the numerical controller and a receiving circuit 4 for receiving machine information from a machine 6. The machine information received by the receiving circuit 4 is inputted to the CPU 1 through a CPU 2 for performing input/output control. The input/output control of the machine information can be performed by the CPU 1 without using the CPU 2.
The machine information outputted from the machine 6 includes information of an operating state of the machine, such as an emergency stop signal.
Since the machine information from the machine is received by the single receiving circuit in the conventional numerical controller, there rises a problem that the machine information is hardly received from the machine when the receiving circuit is in trouble. In particular, if important machine information such as the emergency stop signal is not received, there arises a serious problem with respect to safety.
An object of the present invention is to provide a numerical controller capable of monitoring a receiving circuit to which information from a machine is inputted.
According to the present invention, machine information from the machine is received by a plurality of independent systems and the signals received by the plurality of systems are compared, thereby the receiving state of the receiving circuit is monitored.
The controller of the present invention comprises: a plurality of receiving means provided independently of one another for respectively receiving a signal from the industrial machine; and monitoring means for comparing signals received by the plurality of receiving means and monitoring the receiving means based on a result of the comparison.
The receiving means is provided in the controller and is connected to the industrial machine via an input/output terminal provided in the controller. An external signal represents an external state including an operating state of the machine, such as an emergency stop signal. The receiving means of the present invention receives all or some of the signals outputted from the machine. The monitoring means may be provided with a function of selecting the external signal to be compared, from the signals received by the receiving means, so that a predetermined signal such as an emergency stop signal is selected as the signal to be compared.
The plurality of independent receiving means respectively receives a signal from the industrial machine. If the received signal include a signal to be compared, the monitoring means makes a comparison of the signals received by the plurality of receiving means. In the comparison of the received signals, if the received signals agree with one another, it is determined that the receiving means properly operates. If the external signals disagree with one another, it is determined that the receiving means is in trouble. The monitoring means has a function of notifying the controller or an external equipment about an abnormality of the receiving means. This monitoring means can be constituted by software or hardware.
The receiving means includes a receiving circuit and a signal line for connecting with the industrial machine. Thereby, the controller of the present invention can monitor a receiving system including the receiving circuit and the signal line connected with the industrial machine.
The signal line may connect a numerical controller with a servo amplifier, thereby an existing signal line connected with the numerical controller can be utilized to have an advantage that the numerical controller need not be provided with a new connection port.
According to an aspect of the present invention, the monitoring means is provided commonly to the plurality of receiving means. According to another aspect, a plurality of monitoring means are provided so that each monitoring means is associated with each of the plurality of receiving means. The monitoring means can be constituted by providing a monitoring function in a control circuit of the controller or providing a monitoring circuit independently of the control circuit in the controller.
Further, the monitoring means may constituted by an input/output control circuit between the receiving means and the control circuit of the numerical controller, or a monitoring circuit connected to the receiving means.
In the case where the monitoring means is provided for each receiving means, one of the monitoring means receives a signal received by the receiving means associated with the other monitoring means from the other monitoring means. The one monitoring means compares the signal received by the receiving means associated with the other monitoring means and the signal received by the receiving means associated with the one monitoring means.
Further, the other monitoring means receives a signal received by the receiving means associated with the one monitoring means from the one monitoring means, and compares the signal received by the receiving means associated with the one monitoring means with the signal received by the receiving means associated with the other monitoring means. Thereby, the external signal received by the one monitoring means and the external signal received by the other receiving means are cross-checked. A criterion for the comparison may be set up by a whole agreement or an agreement of majority of the plurality of external signals.